fix(#70): harden the tracked-span revert per branch review

- shiftTracked (pure, anchorer.ts + unit tests): interior/outside edits shift,
  boundary-straddling edits distrust; an insertion exactly at the span start
  lands BEFORE the span (never absorbed into the revert target)
- clear tracked spans on doc close (a closed buffer can change on disk with no
  change events — a kept span could revert over unrelated text, INV-11)
- renderAll only REBUILDS an absent span from an exact resolve; a present entry
  is continuously-tracked ground truth (duplicate-text resolve can't clobber it)
- revertInPlace/finalizeInPlace gain the guard.isReadOnly check (INV-16)
- the hard-fail warning offers 'Discard proposal (leave text)' so a reloaded
  session can still dismiss an unlocatable proposal record
- ✓/✗ CodeLens pair anchors at the tracked span when a tweak orphans the exact
  anchor (the fixed reject path stays reachable from the primary gesture)
- QuickPick batch menu routes through the reporting accept-all/reject-all
  commands (a discarded skip tally re-created the silent failure)
- one clearProposal helper replaces the thrice-copied clear sequence;
  reject() now cleans applied/appliedSpans too

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/anchorer.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { buildFingerprint, resolve, shift, type OffsetRange } from "../src/anchorer";
+import { buildFingerprint, resolve, shift, shiftTracked, type OffsetRange } from "../src/anchorer";
 
 const DOC = "line0\nline1 needle here\nline2\nneedle again on line3\n";
 
@@ -67,3 +67,54 @@ describe("shift", () => {
     expect(shift(r, { start: 3, end: 7, newLength: 1 })).toEqual({ start: 3, end: 7 });
   });
 });
+
+describe("shiftTracked (#70 — tracked applied spans)", () => {
+  const r: OffsetRange = { start: 10, end: 20 };
+
+  it("edit entirely before the span shifts both endpoints by the delta", () => {
+    expect(shiftTracked(r, { start: 0, end: 0, newLength: 3 })).toEqual({ start: 13, end: 23 });
+  });
+
+  it("edit entirely after the span leaves it unchanged", () => {
+    expect(shiftTracked(r, { start: 25, end: 28, newLength: 0 })).toEqual({ start: 10, end: 20 });
+  });
+
+  it("edit fully inside the span keeps the start and grows/shrinks the end", () => {
+    // replace [12,15) with 5 chars (delta = +2)
+    expect(shiftTracked(r, { start: 12, end: 15, newLength: 5 })).toEqual({ start: 10, end: 22 });
+  });
+
+  it("replacing the span's exact full contents is an interior edit", () => {
+    expect(shiftTracked(r, { start: 10, end: 20, newLength: 4 })).toEqual({ start: 10, end: 14 });
+  });
+
+  it("an insertion exactly at the span start lands BEFORE the span (never absorbed)", () => {
+    expect(shiftTracked(r, { start: 10, end: 10, newLength: 6 })).toEqual({ start: 16, end: 26 });
+  });
+
+  it("an insertion exactly at the span end lands AFTER the span (never absorbed)", () => {
+    expect(shiftTracked(r, { start: 20, end: 20, newLength: 6 })).toEqual({ start: 10, end: 20 });
+  });
+
+  it("an insertion at an EMPTY span's point lands before it (deletion-proposal span)", () => {
+    const empty: OffsetRange = { start: 10, end: 10 };
+    expect(shiftTracked(empty, { start: 10, end: 10, newLength: 3 })).toEqual({ start: 13, end: 13 });
+  });
+
+  it("an edit straddling the span's start boundary is distrusted (INV-11)", () => {
+    expect(shiftTracked(r, { start: 8, end: 12, newLength: 0 })).toBe("distrusted");
+  });
+
+  it("an edit straddling the span's end boundary is distrusted (INV-11)", () => {
+    expect(shiftTracked(r, { start: 18, end: 22, newLength: 1 })).toBe("distrusted");
+  });
+
+  it("an edit fully containing the span (e.g. a wholesale replace) is distrusted (INV-11)", () => {
+    expect(shiftTracked(r, { start: 0, end: 30, newLength: 12 })).toBe("distrusted");
+  });
+
+  it("a deletion consuming an EMPTY span's neighborhood is distrusted (INV-11)", () => {
+    const empty: OffsetRange = { start: 10, end: 10 };
+    expect(shiftTracked(empty, { start: 8, end: 12, newLength: 0 })).toBe("distrusted");
+  });
+});